The Janssen COVID-19 vaccine (Ad26.COV2.S) safety study is a retrospective observational Post-Authorisation Safety Study (PASS) using European Healthcare Data through VAC4EU. So far, we have conducted two feasibility analyses: capturing of COVID-19 vaccine use in the different data sources (13.3 million individuals), characteristics of recipients of COVID-19 vaccines and the occurrence of selected adverse events of special interest (AESIs) after receipt of the Ad26.COV2-S vaccine without consideration of disease-specific risk windows. The data from the data sources proved to be fit for the purpose of conducting the planned final analysis of this study. For the final analysis, we will assess the risk of developing AESIs within disease-specific risk windows following the administration of this vaccine.